Composting is the process of creating the ideal conditions for the rapid decomposition of organic materials. Organic materials are things that were once alive, such as most garden and food wastes. In nature, as things die they are consumed and digested by various creatures, from insects to microorganisms. Varying conditions and nature’s slow pace mean decomposition can take a long time. When we make a compost pile from our organic waste, we create the conditions that these decomposer organisms need to thrive.

What Is Compost?
Compost is decomposed organic material that is rich, dark, crumbly, and earthy smelling. It has a soil-like texture and contains many valuable plant nutrients. Compost can be mixed with soil that has been depleted of organic material.

Why Compost?Gardeners spend too much money every year buying topsoil, peat moss, fertilizers, and pesticides. We can take the kitchen scraps and yard waste that we throw away everyday and turn them into compost, which can be used to reduce our dependence on these expensive soil amendments. Compost improves soil texture, allows for easier root growth, helps retain water, contributes plant nutrients, and can aid in pest and disease management. These benefits of compost are why it is often referred to as “chicken soup for the soil” or “black gold.”

The average New York City household throws away two pounds of organic waste each day. This adds up to over one million tons of organic waste per year, most of which is transported to landfills. The transportation of waste is very expensive and causes pollution. When organic waste is buried in landfills, it is cut off from oxygen and decomposers. By throwing away compostable materials we not only use up precious landfill space, we also discard a valuable resource that can help to grow beautiful gardens, lawns, and houseplants.

How Does Compost Happen?
Microorganisms (mostly bacteria) decompose the organic material and turn it into heat, carbon dioxide, water, and compost. Essentially, microorganisms are eating and digesting the organic material. The microscopic decomposers are present on the organic material and in the soil.

How Can I Compost Better?
The decomposers that we want in our compost pile breathe air, are small, work faster at higher temperatures, require water, and need a balanced diet. Knowing these traits allows us to alter the conditions of our compost in order to maximize decomposition.

Particle Size: The smaller you are able to cut up your compostable materials, the more surface is available for the decomposers to chomp up. For example, cutting up leaves with a lawn mower or weed whacker before putting them in the compost pile will help to quicken decomposition.

Temperature: The compost process usually slows down during our cold winters. However, if you have enough material, you can build a pile large enough to trap heat. This type of pile should be at least 3 feet by 3 feet by 3 feet and can get as hot as 160°F. Achieving a high temperature (over 140°F for three days) not only speeds up the composting process but also kills weed seeds and plant diseases. It is okay if you can only build a smaller, cold pile. It will still break down, but over a longer period of time. You can insulate your small pile with leaves, Styrofoam, or bubble wrap to trap some of the heat.

Aeration: The aerobic (oxygen breathing) bacteria are the ones you want in your pile. As the pile compacts, air will be less able to circulate through the pile and anaerobic decomposers can take over. The anaerobic decomposers will produce bad smells as well as acids and alcohols that are toxic to growing plants. In order to avoid this situation you can turn the pile, use an aeration tool, or insert aeration pipes into the center of the pile to make sure oxygen gets into your pile.

Balanced Bacterial Diet: The two main components of your decomposers’ diet are carbon and nitrogen. By volume, you should put in about two-thirds high carbon materials, also know as browns or dry ingredients, and one-third high nitrogen materials, also known as greens or wet ingredients. Carbon materials include leaves, straw, and paper. Nitrogen materials include fresh grass clippings, food scraps, weeds, and garden clippings. If you put in too much carbon, the compost will decompose very slowly because the decomposers need some nitrogen to work. If you add too much nitrogen, the decomposers will work too fast, using all of the available oxygen. Anaerobic bacteria will take over and cause the pile to smell.

Moisture: The microorganism decomposers in your pile live in a thin film of water around their food particles. Your pile should feel moist, but not wet, like a wrung-out sponge. If you squeeze a handful of the compost and more than one or two drops of water drip out, the pile is too wet. The water will block air circulation and decomposition may become anaerobic. To fix wetness, turn the pile as you add dry ingredients.

If the pile is too dry, the decomposers will become dormant and composting will slow down. To fix dryness, turn the pile as you add water.

What Can and Cannot Be Composted?
All organic waste can be composted. However, if you live in a city or residential area, meat, cheese, and fatty products should be avoided because they tend to attract pests and produce bad smells. Other things to avoid are weeds with seeds, plants that regrow from their parts, and plants infected with disease or insects. These bad things could survive the composting process and show up wherever you use the finished compost. Glass, metal, and plastic will not decompose in our lifetimes, but paper and untreated wood products can be composted if chopped up. You should not compost dog and cat waste because they may contain diseases that can be passed on to humans. For more information, see http://www.nyc.gov/nycwasteless/compost.

Where and How Should I Compost?
Where and how you compost depends on the time, space, and materials you have available.

If you have six months to a year and a small yard, you can compost in a bin. Compost bins can be made or purchased. (bins are available to New York City residents through QBG and the City’s other botanical gardens.) A homemade bin can be built with wire fencing, wood, plastic snow fencing, concrete blocks, or wooden shipping pallets. Kitchen scraps and yard waste are mixed together in the bin. Kitchen waste should always be buried under dry ingredients to avoid pests. Also, bins should have a lid or covering, such as a tarp, on top to prevent extreme moisture and a screen underneath to keep out pests.

If you want to make compost more quickly and have compostable materials and more space, you can use a three-bin system. Each bin holds compost in a different stage of decomposition. Fresh waste goes in the first bin. After a month or so, this compost is shoveled into the middle bin. It will stay for there for another month before being turned into the last bin. As the compost is moved from bin to bin, the materials are mixed and aerated, which helps speed up decomposition.

If you have adequate space and can wait a year, you can bury your waste using what is known as incorporation, pit, or trench composting. Simply dig a hole or trench in the ground and fill it with compostables. Make sure your hole is deep enough to cover the waste with at least eight inches of soil to keep out pests. This method is not recommended for areas that have deep burrowing pests like rats.

There is even a composting method for people without any outside space. Vermicomposting, or composting with worms, only requires a small indoor area. After three months you can harvest small amounts of compost whenever you need it. A worm bin is usually a plastic bin that is no deeper than twelve inches with holes for aeration and a fitted lid. You fill the bin with damp shredded paper and then add red wiggler worms (the amount of worms you need depends on the size of your container. After the worms are added, you can add up to a half pound of food scraps per day, making sure to completely bury your food scraps under the paper bedding. The bin can be stored in a kitchen, basement, or garage as long as the temperature stays between 55° and 80°F. As the worms digest the food waste and bedding, they leave castings (a.k.a. worm poop), which are an excellent soil amendment rich in plant nutrients.

Another way to recycle organic materials is mulching. Lawn clippings, pine needles, chipped branches, and bark chips can be placed in pathways, on top of garden beds, and under trees. Mulching helps to block weed growth, prevent soil erosion, insulate soil, and conserve soil moisture. It is not recommended to use woody mulch on garden beds because it will take a long time to break down. Also, pine needles tend to be acidic; they should only be used around acid-loving plants.

How Do I Use Compost?
Compost is great for gardens, lawns, houseplants, street trees, or any other plant because it improves soil structure, holds moisture, holds soil together, and contains beneficial soil life.

Before you use compost, make sure that it is mature. Compost is not ready to use if it is still hot or smells like ammonia, or you can recognize the original material that you added. The simplest way to test your compost’s readiness is to use the bag test, which involves putting a handful of compost in a sealable bag and checking it after a week. If the contents of the bag smell like ammonia or smell sour, then the microorganisms are still working and the compost needs more time.

If your compost is ready, you can use it as is or you can screen it to get a finer compost material for uses that require smaller particles. The best time to apply compost to your garden is when you are preparing the soil for planting. Compost can be applied to shrubs, houseplants, and lawns at any time during the year.

More Questions?
Contact the NYC Compost Project hosted by Queens Botanical Garden staff by email or phone at 718.539.LAWN (5296) with your questions.